This invention relates to an electro-thermal actuator in general and to a valved boiler therefor to produce a snap-action output in particular.
In copending, co-assigned Sobecks application filed concurrently herewith, a fluid displacement actuator is disclosed in which a ported barrier is positioned between the boiler chamber and the actuator chamber. Such ported barrier permits fluid to be displaced therethrough by increased pressure in the boiler chamber to drive the diaphragm and piston assembly through the expansion stroke, the displaced fluid having a lower temperature coefficient heater, thereby to reduce the permeation of the elastomeric diaphragm. Such ported barrier thereby increases the life of the actuator but is relatively slow acting because the entire diaphragm is exposed to the working fluid throughout heater energization.
To provide for a snap-action output, the present invention includes a single valve having a limited diameter bore in the partitiion that opens only when a predetermined, relatively high pressure is attained in the boiler chamber. By building up such high pressures before the valve is opened, substantially the entire diaphragm is rapidly exposed to such relatively high pressures quickly to drive the diaphragm and piston assembly through the expansion stroke with a snap-action effect. This snap-action permits the heater in the boiler chamber to be de-energized immediately upon the desired pressures in the boiler chamber being reached.
It is accordingly the principal object of the invention to provide an electro-thermal actuator having a snap-action output.
It is another object of the invention to provide a partition between the heater and diaphragm, with said partition having a valve therein that opens only when a predetermined pressure in the boiler chamber is achieved. Such valve thus ensures that the diaphragm does not begin its expansion stroke until substantially the entire working surface of the same can be exposed to expanding fluid of predetermined relatively high pressure.
It is still another object of the present invention to provide an electro-thermal actuator having a fast expansion and contraction cycle. This object is accomplished by the snap-action output in combination with a subsequent relatively quick cool down period for the working fluid to permit a rapid, spring loaded contraction stroke. The fluid cool down period is improved by the heater being de-energized before expansion is completed and/or by the relatively cool walls of the previously isolated actuation chamber providing an improved heat exchange effect with such fluid.
Other objects and advantages of the present invention will become apparent as the following description proceeds.